Seasonal and interannual variation in the cross-equatorial meridional currents observed in the eastern Indian Ocean

Observations from moored subsurface acoustic Doppler current profilers (ADCPs) have revealed the structure of cross-equatorial meridional currents in the eastern equatorial Indian Ocean. Using observational data longer than 8 years, we present observations of the seasonal and interannual variation in the cross-equatorial currents in the 2000s. In line with earlier observations and numerical simulations, there were significant subsurface currents that displayed seasonal variation. The annual mean condition was dominated by currents during the boreal summer monsoon in which the Ekman transports are southward on both sides of the equator. The vertical structure of the mean meridional current displayed evidence of a shallow equatorial roll, consisting of northward surface flow and southward subsurface flow above the base of the isothermal mixed layer. The seasonal variation in upper 120 m meridional transport can be explained by wind-driven cross-equatorial Ekman/Sverdrup transport. Interannual variability was higher in the winter monsoon period than in the summer monsoon. The interannual variation could be related to the Pacific El Nino/Southern Oscillation (ENSO). ENSO-induced variation in the southeasterly trade wind could modulate meridional Sverdrup transport. Implications of these observational results for meridional heat transport are discussed.